Unopposed appetite (orexigenic) mechanisms in the near-term ovine fetus: central leptin does not inhibit sucrose ingestion

Abstract

Objective: Leptin is produced in adipocytes and is present in the term fetus. In the adult, leptin acts centrally to inhibit neuropeptide Y-induced carbohydrate intake. We sought to examine if central leptin alters fetal ingestion of oral sucrose in the near-term ovine fetus.Methods: Five pregnant ewes and fetuses were prepared with fetal vascular, sublingual and intracerebroventricular (ICV) catheters and esophageal electromyogram electrodes, and studied at 132 ± 1 days' gestation (term 145–150 days). Following a 2-h baseline period, 10% sucrose was infused sublingually (0.25 ml/min) for the duration of the study. At time 4 h, leptin (0.075 mg/kg) was administered ICV and fetal swallowing was monitored for an additional 6 h.Results: During the basal period, fetal swallowing averaged 0.7 ± 0.1 swallows/min. Fetal swallowing increased significantly in response to 10% sucrose (1.2 ± 0.1 swallows/min; p < 0.05). In response to ICV leptin, fetal swallowing remained significantly elevated at 2, 4 and 6 h (1.3 ± 0.4, 1.4 ± 0.3 and 1.5 ± 0.2 swallows/min, respectively; p < 0.05 vs. control).Conclusions: These results indicate that central leptin inhibition of sucrose ingestion is not functional in the near-term fetus. We speculate that a leptin-mediated anorexigenic response is not present at birth, such that unopposed appetite stimulatory mechanisms in the newborn may facilitate rapid newborn weight gain despite high body fat levels.